1、Vehicle noise vibration and harshnessAbstract Vehicle noise, vibration and harshness (NVH) is usually the major attribute because of its priority in the design of vehicles. NVH affects the design and manufacture process of a vehicle as higher customer satisfaction are attributed by a good NVH behavi

2、or. The research on NVH relies on a variety of computer software to improve and control NVH. In this paper, several vehicle components including rubber dampers and isolators which play an important role in controlling the NVH are presented. A description of source of NVH in a vehicle is shown.Keywor

3、ds: NVH; rubber damper; isolator; research. 1. IntroductionVehicles consist of space vehicles, airplanes, submarines, trains, road, off-road and others 1. Vehicle noise, vibration, and harshness (NVH) is a major problem in the automobile manufacturing process and affects the customer satisfaction of

4、 automobile owners. The researches of vehicle noise, vibration, and harshness (NVH) are not only suitable for the design process of new automobiles, but contribute to improve the comfort and performance of current type of automobiles. Those researches are largely due to the increasing demands of veh

5、icle manufacturers, Original Equipment Manufacturers (OEMs) and customers. The OEMs aim to look for the products that address issues of NVH, reduce vehicle weight, improve stiffness, and are easy to model, lower costs, and are environmentally friendly 2. Automotive noise, vibration and harshness are

6、 the most important issues when the customers assess vehicle quality 1. On the other hand, some manufacturers refuse to corporate automation into vehicle design, as addressing the issues of NVH which makes vehicles too quiet may pose a threat to the safety of pedestrians 4. The vehicular noise can a

7、ct as a warning signal for pedestrians. Some components in the vehicles play important roles in reducing NVH, namely rubber dampers, the power plants, chassis coupling, and elastomeric isolators. Rubber dampers insert between the fins and rubber dampers reduce the amplitude of vibration of fins whic

8、h are used to speed up the heat transfer from the engine surfaces 3. In vehicles, the engine mounts affect largely the noise, vibration, and harshness comfort. The mounts are used to provide supports for the power plant and to isolate the vibrations of the power plant from the rest of the vehicles 6

9、. A multiplicity of elastomeric isolators is needed, including engine mounts, suspension bushings, and frame and sub frame mounts 5. Some functional requirements for isolators involve steering, braking, package, and durability, although these desired characteristics conflict frequently.2. The resear

10、ch on NVHFor vehicles, the issue of vibration, noise, and harshness (NVH) exists mainly in the engine, car body, and engine mounts. During the working of these components, they are affected by aerodynamic (NVH), air-conditioning system (NVH) and brake system (NVH). Vehicle NVH emphasis the feeling o

11、f human beings for vibration and noise and cannot be measured directly. The research on NVH consists of the comfort of passengers in vehicles and intensity problems of vehicles components caused by vibration. The research on the characters of vehicle NVH should concentrate on entire cars and separat

12、e entire cars into subsystems, such as engine system, engine mount system and car body system.The issue of vehicle NVH is not caused by relatively several reasons rather than simply one reason. For instance, the noise in the car may be due to the high level of noise of the engine, the pour isolation

13、 effect of suspension around the engine, or limited technology of sound-proofing between the car body and power system. There are some basic theories and methodologies helping understand and study the character of NVH.Finite element methods are to separate continuous elastomer into the limited numbe

14、r of units and calculate the system deformation, stress, and dynamics character through the finite element models on the computer. Because of the rapid development of finite element methods and the maturity of relative analysis software, FEM has become an essential method to analyze the character of

15、 vehicle NVH. FEM is suitable for the modeling analysis of vehicle body structure vibration and car interior cavity noise. On the other hand, combining FEM with multi-system dynamics to analyze engine mount system can increase the accuracy of dynamic character of the engine mount. BEM is short for t

16、he blade element momentum. Compared with FEM, BEM decreases the dimension of questions, making it convenient to handle the issues of unlimited field and establish the efficient network on the computer. The BEM theory is greatly employed for practical engineering application, especially in the field

17、of NVH 16. The shortage of BEM to address the problem of NVH is low speed of calculation. Experimental transfer path analysis (TPA) is a fairly well established technique for estimating and ranking individual low-frequency noise or vibration contributions via the different structural transmission pa

18、ths from point-coupled powertrain or wheel suspensions to the vehicle body 11. Experimental transfer path analysis is a favored technique to investigate further possibilities to fine-tune the rubber components of the engine and wheel suspension with respect to NVH.The experimental transfer path anal

19、ysis method involves an indirect measurement procedure for estimating operating force components acting at the coupled DOFs (degree of freedom). TPA also involves a direct measurement of all transfer frequency response functions between response in points of interest and points where these forces ac

20、t 11.Design of experiments method (DOE) can be used to minimize the transmitted engine- induced harshness to the body and improve a vehicle body structure. The DOE method includes factorial and response surface methods. The surface modeling is accomplished for the vehicle body with CATIA and HYPERME

21、SH software which is used to create and optimize the FEA modal. NASTRAN software is used to analyze the modal in a frequency range between 0-50Hz 17, 18. 3. The effect of rubber dampers on NVHThe rubber damper is an important type of equipment to reduce noise, vibration, and harshness (NVH), widely

22、being used in a number of machines, vehicles, trains and aircrafts. The popularity of rubber dampers is due to the characteristics of rubber with high visco-elasticity and high elasticity. Compared with steel, elastic deformation of rubber is large and elasticity modulus of rubber is small. As well,

23、 rubber is considered as incompressible material.The function of rubber dampers between the fins is to make a compromise between vibration amplitude increases and fin base temperature decreases. Through the research on the effect of rubber dampers on the radiated noise from engine, it is concluded t

24、hat the effect of the rubber dampers is to reduce engine high frequency noise level, which means the problem of vehicle noise vibration and harshness can be partly handled by using the rubber dampers.Engineers continue to work on the issues of high vehicle noise vibration and harshness when an engin

25、e does not rubber dampers with two methods. These two approaches are related to structural noise problems. The first method is to find ways of reducing the sound power by passive means and the other method is to use active control approaches. Compared with active control solutions which may be suita

26、ble in the future, passive control should not be ignored as it is useful for high frequency noise 3.Rubber dampers are not the only equipment using rubber in vehicles and some rubber connections are widely employed for structural parts. A change in rubber joint material properties can help evaluate

27、the sensitivity of the full- scale system vehicle noise vibration and harshness (NVH) 7. A three level modeling approach with a material, a component, and a system level has been introduced to evaluate the sensitivity of the NVH. 4. powerplant mounting system NVHThe basic function of engine mount is

28、 to support the weight of power train and to isolate the vibration and harshness transmission from engine to body, to segregate the transmission from road surface excitation to power train 8. As well, in order to lighten the car body, increase power-intensive engine and require vibration, noise, and

29、 harshness isolation for passenger cars, the performance of the powerplant mount system need to be improved. Many factors, such as the engine layout state, the supporting positions of chassis mount, the fixed positions on the cylinder of the mount and the layout of surrounding parts, should be consi

30、dered before the designation of engine mount 9. The responses of the powerplant mounting system to low frequency vibrations are important for improving the NVH in terms of rigidity and damping. Some designs of powerplant mounting system try to handle the issues of NVH by concentrating on the positio

31、ning and design of resilient supports. However they fail to consider chassis and suspension system interactions as these designs are based on decoupling rigid body modes from a grounded powerplant mode. Fig.1. Powerplant mounting systemThe traditional engine mount design strategies consider only the

32、 rigid body modes of a grounded engine and arrangements of powerplant rigid body mode 6. When considered as a rigid body, three translational modes and three rotational modes of frame represent the vibration, noise, and harshness (NVH) of powerplant using dynamic decoupling method. In detail, three

33、translational modes are bounce, lateral, and longitudinal vibrations and three rotational modes are called by rotations about pitch, roll and yaw. It is believed that the vibration, noise and harshness (NVH) transferred to the car body structure can be reduced by conditioning the powerplant mounting

34、 system such that the powerplant oscillates about the torque axis 10. The torque roll axis decoupling strategy controls the displacement of the uncoupled blocked powerplant. With less displacement of the powerplant, the level of NVH is reduced 6.The traditional design strategies sometimes may not pu

35、t the issues of vehicle vibration noise and harshness (NVH) into consideration. With the development of technology and increasing demands of customers for comfort, the manufacturers and automobile companies begin to pay attention to design new powerplant mounting system. The current powerplant mount

36、ing strategies examine the rigid-body modes of the power train as it would sit on the mounts attached to the ground and neglect the effect of the chassis. The current engine mount system has achieved the goal that makes sure the driver and the passengers isolate from vibration noise and harshness (N

37、VH) generated by the engine.5. Isolator on NVHElastomeric isolator and hydraulic isolator are widely used in automotive vehicle including shock absorbers, engine mounts and body mounts. Isolators can reduce vibrations and improve the ride performance experienced by drivers and passengers. Noise, vib

38、ration and harshness (NVH) are important to the consumers acceptance of a vehicle. Isolators type, sizing and placement are critical to NVH design 13. The difference between elastomeric isolator and hydraulic isolator is that hydraulic isolators are frequency dependent and elastomeric isolators are

39、independent of frequency. It is largely because they use different mediums to dissipate mechanical energy. A hydraulic isolator connects a vibrating body and an isolated body in a vehicle and consists of a cylinder with two chambers and a piston. An electronic control system is required to cooperate

40、 with hydraulic isolator to supply an alternating current of appropriate amplitude and phase to several magnetic coils disposed adjacent to the tuning slug 12. Matching the isolation frequency with the vibration frequency and adding energy to the vibration isolator to compensate for damping losses i

41、s the basic theory how no vibration is transferred from the vibrating body to the isolated body with the help of hydraulic isolator. Fig 4.1 hydraulic isolatorThe elastomeric isolators in the vehicles are separated into two kinds, namely rubber isolator and metal-net isolator. They are used for engi

42、nes, especially for large power diesel engine. The metal-net isolator with the characters of nonlinear stiffness, large damping and power circumstance adaptability has advantages over rubber isolator and can be used as diesel engines mount component. Rubber isolators have been used in NVH control fo

43、r years. Rubber is hyper elastic material and its suitability as isolator is due to good flexibility and resilience characteristics 14, 15. Rubber isolators cannot be used in low, high temperature, erode and tough circumstance, e.g. in low temperature, rubber isolators have no isolating effect causi

44、ng the aggravation of NVH and also can only isolate a single frequency vibration in any circumstance. It is due to the traditional design depending on experience and repeat experiment. Modern rubber isolator is designed with finite element method 14. A modern rubber isolator is composed of steel and

45、 rubber. What differentiate modern isolator rubbers from traditional rubbers is that there are several holes. Those holes can effectively change the static and dynamic characteristics of rubber isolators. As a result, it manages to improve NVH with the improvement of performance of rubber isolators

46、Fig 4.2 rubber isolatorA metal-net isolator consists of the stainless steel web and the metal wire. When the force is on the stainless steel web, the metal wire slides and results in dry friction damping that absorbs and consumes the energy of system to approach isolating and cushion aims. The isola

47、tors elastic character is nonlinear, which has higher carrying capacity. Active isolation and passive isolation are two kinds of ways to isolate vibration with the use of metal-net isolator. Active isolation reduces vibration by isolating machine from vibration source and passive isolation relaxes t

48、he effect of external vibration 10. Fig 4.3 metal-net isolatorCompared rubber isolator with metal-net isolator, the transfer rate of metal isolator is smaller than that of rubber isolator, which means metal-net isolator has more ability to control NVH and absorb energy. 6. Conclusion Vehicle vibrati

49、on, noise and harshness (NVH) has been receiving considerable attention for many years. The main sources of usual NVH are power engine, brake, suspension system, the steering system as well as other hardware of the vehicle. Also, the road NVH and wind NVH has become important issues as they dominate

50、 the medium and high speed ranges. In order to improve NVH, the performance of rubber dampers and isolator should be taken measured to improve. The paper gives a brief description of the current research of NVH, several modern methods such as finite element method and blade element momentum have alr

51、eady put into use. These methods greatly increase the accuracy and efficiency when addressing the issues of NVH.Two major components in a vehicle used to control NVH are introduced in the paper, namely rubber damper and isolator. The effect of rubber dampers is to isolate the engine NVH. Isolators a

52、re widely used in a vehicle and can be separated as elastomeric isolator and hydraulic isolator. The metal-net isolator has more advantage than rubber dampers. Engine and engine mount are the main sources of NVH. Some traditional engine mounting systems have shortages in design and manufacture. Refe

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54、he effect of rubber dampers on engines NVH and thermal performance” , Applied Acoustics 75 17-26 (2014).4 Nicholas D. Cottrell and Benjamin K. Barton. “The impact of artificial vehicle sounds for pedestrians on driver stress” ,Ergonomics, Vol.55, 1476-1486 (2012).5 Himes, R.S. and David Griffiths. “

55、Future vehicle noise, vibration and harshness requirements for elastomeric isolators”, the Detroit Rubber Group meeting, Detroit, the USA, September 20006 Courteille, E., Leotoing, L., Mortier, F. and Ragnean, E. “New analytical method to evaluate the power plant and chassis coupling in the improvement vehicle NVH”, European Journal of Mechanics A/Solids